1. Field of the Invention
The present invention generally relates to a lighting control apparatus of a vehicle-purpose lighting device. More specifically, the present invention is directed to a lighting control apparatus of a vehicle-purpose lighting device, which is arranged in such a manner that lighting operations of a semiconductor light source constituted by a semiconductor light emitting element are controlled.
2. Background Art
Conventionally, light sources are known in which semiconductor light emitting elements such as LEDs (Light Emitting Diodes) are employed as vehicle-purpose lighting devices. In such vehicle-purpose lighting devices, lighting control apparatus for controlling lighting operations of the LEDs have been included.
When LEDs are employed as light sources of vehicle-purpose lighting devices, dimming control operations of the light sources can be carried out in an easy manner. However, when LEDs are employed as vehicle-purpose head lamps, there is a possibility that these LEDs cannot properly emit light due to increases in the temperature within the light chambers. As a consequence, it has been proposed that in the case that LEDs are employed in a light source of a vehicle-purpose lighting device, when a speed of a vehicle is decreased from a preset vehicle speed, or when a temperature of the vehicle-purpose lighting device exceeds a threshold value, the currents of these LEDs are decreased so as to suppress heat originally generated from the LEDs (refer to patent publication 1). In this case, even when the current supplied to the LEDs is decreased, the beam attenuations of these LEDs can be carried out, while the light of the LEDs does not disappear.
[Patent Publication 1] JP-A-2004-276737 (FIG. 3 and FIG. 4, pages 4 to 8)
Because heat resistant temperatures of semiconductor light sources, such as LEDs, are low, which is different from those of halogen lamps and discharge lamps, when lifetimes and deteriorations of these semiconductor light sources are considered, beam attenuating operations of the semiconductor light sources may achieve certain effects, for example, suppressions of temperature increases in the semiconductor light sources.
Further, in the case that the beams of the semiconductor light sources are attenuated, if this beam attenuation is simply performed, then energy saving effects may be achieved. However, it is practically difficult to maintain safety characteristics of the semiconductor light sources, particularly with respect to the degrees of luminous intensity distributions.